1. Field of the Invention
The present invention is related to a paper supply apparatus that feeds a print medium such as paper from a paper tray, and conveys the print medium to an image forming unit provided at a downstream side.
2. Description of the Related Art
Conventionally, inkjet printing apparatuses that convey a print medium such as paper and film, and administer printing by jetting ink onto the print medium from an ink head have been proposed.
In such inkjet printing apparatuses, paper supply intervals among print media which are sequentially conveyed from a paper tray are narrowed in order to improve productivity. A printing process that administers printing onto a print medium is conducted simultaneously with a paper supply operation of a next print medium.
For this reason, if vibrations which are generated in the paper supply operation of the next print medium is transferred to an image forming unit that includes the ink jet head, the landing positions of ink which is jetted from the ink head may shift, and there are cases in which errors such as blurring will be generated in a printed image.
Hereinafter, the factors that cause vibrations to be generated during the paper supply operation will be described. FIG. 8 is a schematic diagram for explaining the paper supply operation of a conventional inkjet printing apparatus.
In a conventional inkjet printing apparatus, first, a print medium P1 which is fed out from a paper tray is conveyed by being clamped between a paper supply roller 106, which is a primary paper supply roller, and a sorting plate 105. Then, the leading end of the print medium P1 which is conveyed by the paper supply roller 106 abuts resist rollers 108 and conveyance is temporarily ceased. Thereby, a flexure is formed in the print medium P1 at the position of the resist rollers 108. The resist rollers 108 rotate at a predetermined timing after this flexure is formed, and thereby the print medium P1 is conveyed toward a conveyor belt 202 provided at a downstream side at a desired timing, and is transferred to the conveyor belt 202. The conveyor belt 202 is an annular belt which is wound about rollers 204. The conveyor belt 202 conveys the print medium by suction or by electrostatic adsorption. Ink is jetted toward the print medium from ink heads 206 while the print medium is conveyed, to conduct printing. Note that the element denoted by P0 in FIG. 8 is a print medium which was supplied prior to the print medium P1. As described above, a printing operation onto the print medium P0 and paper supply of the next print medium P1 are conducted simultaneously.
Here, in conveyance control of the print medium as described above, control is exerted such that the conveyance speed of the resist rollers 108 is greater than the conveyance speed of the paper supply roller 106, and the print medium P1 is conveyed while the aforementioned flexure is gradually eliminated. However, because this operation is that in a state in which the resist rollers 108 pull the print medium P1, which is clamped between the paper supply roller 106 and the sorting plate 105, back tension will be generated in the print medium P1 at a point in time when the flexure is completely eliminated. As a result, vibrations and noise will be generated.
Japanese Unexamined Patent Publication No. 2010-215389 proposes a method for preventing such vibrations and noise from being generated. In this method, assist control, by which the degree of acceleration or the conveyance speed of a resist roller and a primary paper supply roller on an upstream side thereof is controlled while resist rollers convey a print medium, is executed in order to assist conveyance of the print medium by the resist rollers.
FIG. 9 is a diagram that illustrates a conventional example of the conveyance speeds of resist rollers and a primary paper supply roller when assist control is executed. In FIG. 9, (S) represents the conveyance speed of the resist rollers, and (Q) represents the conveyance speed of the primary paper supply roller during execution of assist control. In addition, in FIG. 9, (R) represents simulation results of an amount of flexure formed in a print medium at the position of the resist rollers in the case that the conveyance speeds of the primary paper supply roller and the resist rollers are controlled to be (S) and (Q).
In the conventional example illustrated in FIG. 9, assist control of the primary paper supply roller is initiated at a time t0, which is a predetermined amount of time after rotation of the resist rollers is initiated at a predetermined timing. Specifically, the primary paper supply roller initiates rotation at a predetermined degree of acceleration, and assists conveyance of the print medium at a conveyance speed represented by (Q) of FIG. 9.
Thereafter, the conveyance speed of the resist rollers is controlled to be a constant seed from a time t1 of FIG. 9, and deceleration of the primary supply roller is initiated from a time t2.
Then, at a time t3 illustrated in FIG. 9, rotation of the primary paper supply roller is ceased, that is, assist control is completed. Thereafter, deceleration of the resist rollers is initiated from a time t4, and the conveyance speed of the resist rollers is controlled to be a constant speed at a time t5. The constant speed at the time t5 and thereafter, is set in advance to be the same speed as the conveyance speed of a conveyor belt provided downstream, and the print medium is transferred from the resist rollers to the conveyor belt.
According to the conventional example illustrated in FIG. 9, back tension which is generated in the print medium between the primary paper supply roller and the resist rollers can be reduced. Thereby, the aforementioned vibrations and noise can be suppressed.